1. Field of the Invention
The present invention relates to apparatus for purifying contaminated liquids and more particularly to an apparatus for electrochemical purification of contaminated liquids.
The invention may be employed for purifying liquids contaminated with organic substances, mechanical suspensions, surfactancts, and the like.
The invention is particularly useful for purifying liquids contaminated with polymers and petroleum products, such as waste water containing cutting fluids.
2. Description of the Prior Art
Of all the prior art devices for purifying contaminated liquids, the widest and ever increasing application has recently been found by apparatus for electrochemical purification of liquids, in particular those where liquid is purified by the electroflotation and electrocoagulation methods, which is due to their high performance capabilities.
Apparatus are known where the electrochemical liquid purification process is accomplished either in batches, or continuously; the latter appear to be more promising.
A prior art apparatus for electrochemical purification of contaminated liquids (USSR Inventor's Certificate No. 407,844) comprises a settling chamber which houses an electrocoagulation chamber and communicates with the latter. The electrocoagulation chamber has soluble electrodes and an inlet pipe to feed contaminated liquid, disposed under the electrodes. The settling chamber comprises an outlet pipe to discharge purified liquid. In the course of purification, the contaminated liquid with electrolyzing additives (hydrochloric acid, sodium chloride) passes between the soluble electrodes whereto electric current is applied. This brings about the formation of hydroxides of the soluble electrode metal, which coagulate impurities contained in the liquid being purified. From the electrocoagulation chamber, the liquid passes into the settling chamber where sludge separates from the liquid, following which the sludge and the liquid are discharged separately.
Passing between the electrodes, the liquid being purified fouls these, which accelerates passivation of the electrodes and hence increases the power consumption and necessitates frequent cleaning of the electrodes, i.e. eventually reduces the efficiency of the apparatus.
In another prior art apparatus (Japanese Pat. No. 52-14397, published Nov. 30, 1977), the electrocoagulation chamber serves only to produce coagulants, for which purpose a pure electrolyte is fed thereinto, while liquid purification is accomplished in another chamber whereinto the liquid being purified is fed and where the liquid is mixed with the electrolyte containing coagulants and fed from the electrocoagulation chamber.
While greatly diminishing the fouling of the electrode surfaces, such a construction of the apparatus fails fully to exploit the coagulation and flotation capabilities of the electrodes, since when the electrolyte passes from the electrocoagulation chamber to the settling chamber, the coagulants (hydroxides of the soluble electrode metal) and gas bubbles forming on the soluble electrode surface aggregate, which reduces their specific surface and hence impairs their coagulating and flotation capabilities.
The above factors adversely affect the apparatus efficiency, since a considerable part of formed coagulants and gas bubbles take no part in the purification process.
Also known in the art are apparatus wherein contaminated liquid is fed into the electrocoagulation chamber through an inlet pipe disposed above the electrodes, while the electrolyte is passed between the electrodes.
Liquid purification in such apparatus is accomplished with essentially no fouling of the electrodes and a lesser detrioration of the capability of the electrodes to form coagulants and gas bubbles. Hence, a higher efficiency than in the previously described apparatus is ensured. For example, an apparatus for electrochemical purification of contaminated liquids, disclosed in USSR Inventor's Certificate No. 644,738, comprises a settling chamber with an outlet pipe to discharge purified liquid and a tubular electrocoagulation chamber installed in the settling chamber and communicating therewith, at the bottom portion of the settling chamber a system of soluble electrodes is disposed which is provided with an inlet pipe to feed contaminated liquid, disposed above said system of soluble electrodes.
The inlet pipe to feed contaminated liquid should be spaced from the electrodes at such a distance which excludes the possibility of fouling them by impurities contained in contaminated liquid. Thus, when the inlet pipe is of a cylindrical configuration, the distance should be of (1 to 7)d, where d is a diameter of the inlet pipe.
A disadvantage of this apparatus lies in a low purification efficiency and a higher consumption of both soluble electrodes and power, especially in treating heavily contaminated liquids (with an impurity concentration of 2,000 mg/l and higher). Such a liquid is treated at a high current density (1.5 to 2.5 A/dm.sup.2); this causes a large amount of foam to be formed (up to 30 to 40% of the volume of the liquid being treated) containing the hydroxide of the soluble electrode metal (10 to 15%), which features a good sorbing and coagulating capability; however, the foamy product in such an apparatus is not used and is discharged from the apparatus as it accumulates therein.